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  • Special Mixture Design Considerations and Methods for WMA

    Mix Design Practices for Warm Mix Asphalt

    1

  • Special Mixture Design Considerations and Methods for WMA

    Presentations Ramon Bonaquist

    Overview of Proposed Appendix to AASHTO R35 for WMA

    Brian Prowell Data from NCHRP Project 9-47A evaluating

    the Proposed Appendix

    Rick Harvey Efforts to incorporate the Proposed Appendix

    into the AASHTO Standard Methods of Test.

  • Special Mixture Design Considerations and Methods for WMA

    Special Mixture Design Considerations and Methods for

    Warm Mix Asphalt (WMA)

    An Appendix to AASHTO R35Standard Practice for Superpave

    Volumetric Design for Hot-Mix Asphalt (HMA)

    1

  • Special Mixture Design Considerations and Methods for WMA

    Outline Brief Overview of NCHRP Project 9-43 NCHRP Project 9-43 Conclusions NCHRP Project 9-43 Products Review of the Proposed Appendix to

    AASHTO R35 Major Sections NCHRP 9-43 Research

    What to Expect When Using the Appendix

  • Special Mixture Design Considerations and Methods for WMA

    NCHRP 9-43 Mix Design Practices for Warm Mix

    Asphalt Objective

    To adapt laboratory mixture design and analysis procedures to WMA Compatible with HMA procedures Address wide range of warm mix processes

  • Special Mixture Design Considerations and Methods for WMA

    NCHRP 9-43 Approach

    Preliminary Procedure Focus

    Phase I Experiments Reheating Binder Grade RAP Short-Term

    Conditioning Workability

    Revised Procedure

    Phase II Experiments Expanded RAP

    Mixing Laboratory Mix

    Design Field Validation Limited Fatigue

    Final Procedure Draft Appendix

    to AASHTO R35

  • Special Mixture Design Considerations and Methods for WMA

    NCHRP 9-43 Conclusion 1 WMA can be designed with only minor

    changes to AASHTO R35 Specimen fabrication procedures Coating and compactability in lieu of

    viscosity based mixing and compaction temperatures

  • Special Mixture Design Considerations and Methods for WMA

    NCHRP 9-43 Conclusion 2 For mixtures using the same aggregates

    and binders and having binder absorption equal to or less than 1 percent Volumetric properties of WMA and HMA are

    very similar Compactability, moisture sensitivity, and

    rutting resistance may be different when designed as WMA compared to HMA

  • Special Mixture Design Considerations and Methods for WMA

    NCHRP 9-43 Conclusion 3 Fatigue properties of HMA and WMA are

    very similar

  • Special Mixture Design Considerations and Methods for WMA

    NCHRP 9-43 Products NCHRP Report 691 Recommended Draft Appendix to AASHTO

    R35, Special Mixture Design Considerations and Methods for Warm Mix Asphalt (WMA)

    Commentary to the Draft Appendix Training Materials for the Draft Appendix

    NHI Web-Course ~ September 2011

  • Special Mixture Design Considerations and Methods for WMA

    1. Equipment for Designing WMA,2. WMA Process Selection,3. Binder Grade Selection,4. RAP in WMA,5. Process Specific Specimen

    Fabrication Procedures,6. Evaluation of Coating 7. Evaluation of Compactability, 8. Evaluation of Moisture

    Sensitivity, 9. Evaluation of Rutting

    Resistance, and10. Adjusting the Mixture to Meet

    Specification Requirements.

  • Special Mixture Design Considerations and Methods for WMA

    1 Additional EquipmentLow Shear Mixer to Blend Additive into Binder

  • Special Mixture Design Considerations and Methods for WMA

    1 Additional EquipmentMechanical Mixer Needed of All WMA Designs

  • Special Mixture Design Considerations and Methods for WMA

    1 Additional Equipment

    Laboratory Foaming Device Needed for Plane Foaming Processes

  • Special Mixture Design Considerations and Methods for WMA

    2 WMA Process Selection WMA mix design requires the producer to

    select WMA process Planned production temperature Planned compaction temperature

    Laboratory specimen fabrication

  • Special Mixture Design Considerations and Methods for WMA

    2 WMA Process Selection Producer should consider

    Agency specifications Past performance and technical support Cost Useful temperature range Production rates Modifications

  • Special Mixture Design Considerations and Methods for WMA

    3 Binder Grade Selection Use same grade as HMA

    -6.0 0.0 6.0

    Advera -47 F

    Evotherm -50 F

    Plant Foam -60 F

    LEA -100 F

    Sasobit -47 F

    Change in Grade (HMA Control - WMA), oC

    Low Temeprature Grade High Temperature Grade

  • Special Mixture Design Considerations and Methods for WMA

    4 RAP RAP Does Mix at WMA Temperatures

    Atomic Force Microscope Interfacial Mixing Study

    Laboratory Blending Studies Measured Dynamic Modulus to Estimated Dynamic

    Modulus for Fully Blended Condition

    Mechanism New Coats RAP, Then Continues to Mix While

    Held at Elevated Temperature

  • Special Mixture Design Considerations and Methods for WMA

    4 RAP

    0.00

    0.20

    0.40

    0.60

    0.80

    1.00

    1.20

    0 0.5 1 1.5 2 2.5

    Mea

    sure

    d to

    Hirs

    ch E

    stim

    ated

    Ful

    ly

    Ble

    nded

    Dyn

    amic

    Mod

    ulus

    , 68

    F, 1

    .0 H

    z

    Short-Term Conditioning Time, hr

    HMA 280/255HMA 248/230WMA 248/230WMA 230/212No RAP

  • Special Mixture Design Considerations and Methods for WMA

    4 RAP To Ensure Adequate Mixing

    High temperature grade of RAP

  • Special Mixture Design Considerations and Methods for WMA

    4 RAP

    160

    180

    200

    220

    240

    260

    280

    300

    320

    76 88 100 112 124 136 148 160

    WM

    A Co

    mpa

    ctio

    n Te

    mpe

    ratu

    re, o

    F

    RAP High Temperature Grade, oC

    RAS

    RAP

  • Special Mixture Design Considerations and Methods for WMA

    Low Temperature Grade Improvement for Blending Chart Analysis

    4 RAP

    -6.0 0.0 6.0

    Advera -47 F

    Evotherm -50 F

    Plant Foam -60 F

    LEA -100 F

    Sasobit -47 F

    Change in Grade (HMA Control - WMA), oC

    Low Temeprature Grade High Temperature Grade

  • Special Mixture Design Considerations and Methods for WMA

    4 RAP

    -28

    -22

    -16

    0 20 40 60 80 100

    Low

    Tem

    pera

    tue

    Grad

    e, o C

    RAP Binder Content, %

    32 % 40%

    -0.5

  • Special Mixture Design Considerations and Methods for WMA

    5 Specimen Fabrication

    Additive Added to the Binder

  • Special Mixture Design Considerations and Methods for WMA

    5 Specimen Fabrication

    Additive Added to the Mixture

  • Special Mixture Design Considerations and Methods for WMA

    5 Specimen Fabrication

    Wet Aggregate Mixtures

  • Special Mixture Design Considerations and Methods for WMA

    5 Specimen Fabrication

    Foamed Asphalt Mixtures

  • Special Mixture Design Considerations and Methods for WMA

    5 Specimen Fabrication Short-Term Conditioning

    2 hours at Planned Compaction Temperature

    Compactive Effort and Volumetric Criteria Same as HMA

  • Special Mixture Design Considerations and Methods for WMA

    6 Coating Separate coarse

    aggregates 9.5 mm sieve for NMAS 12.5

    mm and larger 4.75 mm sieve for NMAS 9.5

    and smaller Min 200 particles

    >= 95 percent

  • Special Mixture Design Considerations and Methods for WMA

    6 Coating Differences Observed for

    Planetary vs Bucket Mixers Mixing Times in Appendix

    Based on Planetary Mixer May Require Adjustment

    for Bucket Mixers

  • Special Mixture Design Considerations and Methods for WMA

    7 Compactability Compact 2 specimens to Ndesign at

    the planned compaction temperature Compute gyrations to 92 % of Gmm

    Compact 2 specimens to Ndesign at 30 oC below the planned compaction temperature Compute gyrations to 92 % of Gmm

  • Special Mixture Design Considerations and Methods for WMA

    7 Compactability Why 30 C and 25 % Increase?

    0

    5

    10

    15

    20

    25

    30

    35

    HMA Advera Sasobit

    % In

    crea

    se in

    Gyr

    atio

    ns t

    o 92

    % o

    f G

    mm

    fo

    r 30

    C

    Redu

    ctio

    n in

    Tem

    pera

    ture

    Mixture Type

  • Special Mixture Design Considerations and Methods for WMA

    8 Moisture Sensitivity AASHTO T283

    Short-Term Condition 2 hours at Compaction Temperature

    TSR>= 0.80 with no visual stripping

  • Special Mixture Design Considerations and Methods for WMA

    9 Rutting Resistance Flow Number AASHTO

    TP 79 Short-Term Condition 2

    hours at Compaction Temperature

    Traffic Level, Million ESALs

    Minimum Flow Number

  • Special Mixture Design Considerations and Methods for WMA

    9 Rutting Resistance Testing Conditions

    Air Voids = 7.0 +/- 0.5 percent Temperature = 50 % reliability high pavement

    temperature from LTPPBind 3.1 Depth of 20 mm for surface courses, top of layer

    for intermediate and base courses No adjustments for traffic or speed

    Unconfined 600 kPa repeated deviator stress, 30 kPa

    contact deviator stress

  • Special Mixture Design Considerations and Methods for WMA

    10 Adjustments Coating Compactability Moisture Sen

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